U.S. patent number 10,106,386 [Application Number 15/152,012] was granted by the patent office on 2018-10-23 for hydraulic control device of a forklift truck.
This patent grant is currently assigned to KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. The grantee listed for this patent is KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. Invention is credited to Tetsuya Goto, Takanori Kanna, Tsutomu Matsuo, Yuki Ueda, Takashi Uno, Naoya Yokomachi.
United States Patent |
10,106,386 |
Ueda , et al. |
October 23, 2018 |
Hydraulic control device of a forklift truck
Abstract
A hydraulic control device of a forklift truck includes a first
hydraulic cylinder, a first instruction member, a second hydraulic
cylinder, a second instruction member, a hydraulic pump, an
electric motor, a first passage which has a drain passage, a
lowering control valve that controls flow of hydraulic oil, a flow
rate control valve, and a controller. When a lowering operation of
forks and an operation of a hydraulically-operated unit are
performed simultaneously, when a required rotation speed of the
hydraulic pump that is required for operating the
hydraulically-operated unit at an instruction speed based on an
operation of the second instruction member is a specified rotation
speed or lower, the controller controls an instruction rotation
speed of the electric motor so as to operate the hydraulic pump at
the required rotation speed to thereby restrict the operation of
the hydraulic pump.
Inventors: |
Ueda; Yuki (Aichi-ken,
JP), Yokomachi; Naoya (Aichi-ken, JP),
Matsuo; Tsutomu (Aichi-ken, JP), Uno; Takashi
(Aichi-ken, JP), Goto; Tetsuya (Aichi-ken,
JP), Kanna; Takanori (Aichi-ken, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOYOTA JIDOSHOKKI |
Kariya-shi, Aichi-ken |
N/A |
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOYOTA
JIDOSHOKKI (Kariya-shi, Aichi-ken, JP)
|
Family
ID: |
55919738 |
Appl.
No.: |
15/152,012 |
Filed: |
May 11, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20160332854 A1 |
Nov 17, 2016 |
|
Foreign Application Priority Data
|
|
|
|
|
May 14, 2015 [JP] |
|
|
2015-099226 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F15B
11/161 (20130101); F15B 13/06 (20130101); B66F
9/22 (20130101); F15B 13/021 (20130101); B66F
9/205 (20130101); F15B 2211/40576 (20130101); F15B
2211/20515 (20130101) |
Current International
Class: |
B66F
9/20 (20060101); F15B 11/16 (20060101); B66F
9/22 (20060101); F15B 13/02 (20060101); F15B
13/06 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2818446 |
|
Dec 2014 |
|
EP |
|
02-231398 |
|
Sep 1990 |
|
JP |
|
2013133196 |
|
Jul 2013 |
|
JP |
|
Other References
Communication dated Oct. 20, 2016 from the European Patent Office
in counterpart application No. 16168693.6. cited by
applicant.
|
Primary Examiner: Leslie; Michael
Assistant Examiner: Teka; Abiy
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A hydraulic control device of a forklift truck comprising: a
first hydraulic cylinder that lifts and lowers forks of the
forklift truck; a first instruction member that instructs lifting
and lowering operation of the forks; a second hydraulic cylinder
that operates a hydraulically-operated unit other than the forks; a
second instruction member that instructs operation of the
hydraulically-operated unit; a hydraulic pump that supplies
hydraulic oil to the first hydraulic cylinder and the second
hydraulic cylinder; an electric motor that is connected to the
hydraulic pump and causes the hydraulic pump to operate; a first
passage through which the first hydraulic cylinder and an intake
port of the hydraulic pump are connected to each other; a lowering
control valve that is disposed in the first passage and allows flow
of hydraulic oil from the first hydraulic cylinder toward the
hydraulic pump while the forks are being lowered and that blocks
the flow of hydraulic oil from the first hydraulic cylinder toward
the hydraulic pump while the forks are being lifted or at a stop; a
drain passage that is branched from the first passage at a portion
between the lowering control valve and the hydraulic pump; a flow
rate control valve that is disposed in the drain passage and
controls a flow rate of hydraulic oil; and a controller that
controls the electric motor based on an operation of the first
instruction member and an operation of the second instruction
member, wherein in a case of a simultaneous operation mode in which
a lowering operation of the forks and an operation of the
hydraulically-operated unit are performed simultaneously, when a
required rotation speed of the hydraulic pump required for
operating the hydraulically-operated unit at an instruction speed
based on the operation of the second instruction member is a
specified rotation speed or lower, the controller controls an
instruction rotation speed of the electric motor so as to operate
the hydraulic pump at the required rotation speed, and when the
required rotation speed of the hydraulic pump is higher than the
specified rotation speed, the controller controls the instruction
rotation speed of the electric motor so as to operate the hydraulic
pump at the specified rotation speed to thereby restrict the
operation of the hydraulic pump.
2. The hydraulic control device of the forklift truck according to
claim 1, wherein, during a period between a time at which the
simultaneous operation mode is changed to a single operation mode
in which the operation of the hydraulically-operated unit is solely
performed and a time at which the operation of the second
instruction member is finished, when the required rotation speed of
the hydraulic pump that is required for operating the
hydraulically-operated unit at the instruction speed based on the
operation of the second instruction member is the specified
rotation speed or lower, the controller controls the instruction
rotation speed of the electric motor to thereby operate the
hydraulic pump at the required rotation speed, and when the
required rotation speed is higher than the specified rotation
speed, the controller controls the instruction rotation speed of
the electric motor to thereby operate the hydraulic pump at the
specified rotation speed.
3. The hydraulic control device of the forklift truck according to
claim 1, wherein in the case of the simultaneous operation mode,
the controller sets, as the specified rotation speed, the required
rotation speed of the hydraulic pump that is required for the
lowering operation of the forks at the instruction speed based on
the operation of the first instruction member at a time when the
simultaneous operation mode is started.
4. The hydraulic control device of the forklift truck according to
claim 3, wherein when, in response to an increase of the
instruction speed based on the operation of the first instruction
member, the required rotation speed of the hydraulic pump required
for the lowering operation of the forks at the instruction speed
exceeds the specified rotation speed that is set at the time when
the simultaneous operation mode is started, the controller changes
the specified rotation speed to the required rotation speed.
5. The hydraulic control device of the forklift truck according to
claim 1, wherein the specified rotation speed is a fixed rotation
speed that is lower than the required rotation speed of the
hydraulic pump that is required for operating the
hydraulically-operated unit at a highest instruction speed based on
the operation of the second instruction member, and in the case of
the simultaneous operation mode, when the required rotation speed
of the hydraulic pump that is required for the lowering operation
of the forks at the instruction speed based on the operation of the
first instruction member at a time when the simultaneous operation
mode is started is higher than the fixed rotation speed, the
controller controls the instruction rotation speed of the electric
motor so as to operate the hydraulic pump at the required rotation
speed that is required for operating the hydraulically-operated
unit at the instruction speed based on the operation of the second
instruction member.
6. The hydraulic control device of the forklift truck according to
claim 1, wherein the lowering control valve is a proportional valve
whose opening is variable, and when the operation amount of the
first instruction member is smaller than a specified operation
amount, the controller controls the instruction rotation speed of
the electric motor so as to operate the hydraulic pump at the
required rotation speed that is required for operating the
hydraulically-operated unit at the instruction speed based on the
operation of the second instruction member.
7. The hydraulic control device of the forklift truck according to
claim 1, comprising: a plurality of the hydraulically-operated
unit; a plurality of the second hydraulic cylinder which operates
the respective hydraulically-operated units; and a plurality of the
second instruction member which instructs operation of the
respective hydraulically-operated unit, wherein in a case of an
operation mode in which two or more of the hydraulically-operated
units are operated simultaneously with the lowering operation of
the forks, the controller calculates required rotation speeds of
the hydraulic pump required for operating the respective two or
more hydraulically-operated units at their respective instruction
speeds based on operations of their respective second instruction
members, and controls the instruction rotation speed of the
electric motor so as to operate the hydraulic pump at the required
rotation speed which is the highest of the calculated required
rotation speeds.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic control device of a
forklift truck.
A forklift truck generally uses a hydraulic cylinder as a mechanism
for operating movable loading members of the forklift truck such as
forks. For example, Japanese Unexamined Patent Application
Publication No. H02-231398 discloses a hydraulic control device
having a single hydraulic pump and a single electric motor that
drives the hydraulic pump. The hydraulic pump is driven to rotate
so as to operate hydraulic cylinders (lift cylinders) that lift and
lower the forks and hydraulic cylinders (tilt cylinders) that tit
the mast assembly of the forklift truck.
When a hydraulic control device which has a single hydraulic pump
operates any selected one of a plurality of movable loading
members, the hydraulic control device controls the operation of the
hydraulic pump in accordance with a speed that is instructed for
operating the selected loading member. However, when the hydraulic
control device operates a plurality of movable loading members
simultaneously, the hydraulic control device controls the operation
of the hydraulic pump in accordance with a speed that is instructed
for any specific one of the loading members, and it is difficult to
operate the plural loading members at their respective instructed
speeds.
The present invention, which has been made in view of the problem
above, is directed to providing a hydraulic control device of a
forklift truck that is capable of operating a plurality of loading
members in a desired manner.
SUMMARY OF THE INVENTION
In accordance with an aspect of the present invention, there is
provided a hydraulic control device of a forklift truck that
includes a first hydraulic cylinder that lifts and lowers forks of
the forklift truck, a first instruction member that instructs
lifting and lowering operation of the forks, a second hydraulic
cylinder that operates a hydraulically-operated unit other than the
forks, a second instruction member that instructs operation of the
hydraulically-operated unit, a hydraulic pump that supplies
hydraulic oil to the first hydraulic cylinder and the second
hydraulic cylinder, an electric motor that is connected to the
hydraulic pump and causes the hydraulic pump to operate, a first
passage through which the first hydraulic cylinder and an intake
port of the hydraulic pump are connected to each other, a lowering
control valve that is disposed in the first passage and allows flow
of hydraulic oil from the first hydraulic cylinder toward the
hydraulic pump while the forks are being lowered and that blocks
the flow of hydraulic oil from the first hydraulic cylinder toward
the hydraulic pump while the forks are being lifted or at a stop,
the first passage having a drain passage that is branched from the
first passage at a portion between the lowering control valve and
the hydraulic pump, a flow rate control valve that is disposed in
the drain passage and controls a flow rate of hydraulic oil, and a
controller that controls the electric motor based on operation of
the first instruction member and the second instruction member. In
a case of a simultaneous operation mode in which a lowering
operation of the forks and an operation of the
hydraulically-operated unit are performed simultaneously, when a
required rotation speed of the hydraulic pump that is required for
operating the hydraulically-operated unit at an instruction speed
based on the operation of the second instruction member is a
specified rotation speed or lower, the controller controls an
instruction rotation speed of the electric motor so as to operate
the hydraulic pump at the required rotation speed, and when the
required rotation speed of the hydraulic pump is higher than the
specified rotation speed, the controller controls the instruction
rotation speed of the electric motor so as to operate the hydraulic
pump at the specified rotation speed to thereby restrict the
operation of the hydraulic pump.
Other aspects and advantages of the invention will become apparent
from the following description, taken in conjunction with the
accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a forklift truck having a hydraulic
control device according to an embodiment of the present
invention;
FIG. 2 is a graph showing a relationship among the opening of a
valve, the rotation speed of a hydraulic pump and the cylinder flow
rate in the flow control device of the embodiment;
FIG. 3 is a circuit diagram of the hydraulic control device of the
forklift truck of FIG. 1;
FIG. 4A is a graph showing the operation amount of the control
lever in the hydraulic control device according to a first
embodiment;
FIG. 4B is a graph showing the rotation speed of the hydraulic pump
of in the hydraulic control device according to the first
embodiment;
FIG. 4C is a graph showing the operation speed of forks and
hydraulically-operated loading unit in the hydraulic control device
according to the first embodiment;
FIG. 5A is a graph showing the operation amount of the control
levers in the hydraulic control device according to a second
embodiment of the present invention;
FIG. 5B is a graph showing the rotation speed of a hydraulic pump
in the hydraulic control device according to the second
embodiment;
FIG. 5C is a graph showing the operation speed of forks and
hydraulically-operated loading unit in the hydraulic control device
according to the second embodiment; and
FIG. 6 is a circuit diagram showing a part of a hydraulic control
device according to another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
First Embodiment
A first embodiment of a hydraulic control device of a forklift
truck will now be described with reference to FIGS. 1 to 4.
Referring to FIG. 1, numeral 11 generally designates a forklift
truck that includes a vehicle frame 12, and a mast assembly 13 that
is mounted at a front of the vehicle frame 12. The mast assembly 13
includes a pair of right and left outer masts 13A (only one outer
mast being shown in FIG. 1) and a pair of right and left inner
masts 13B (only one inner mast being shown in FIG. 1) that are
mounted inward of the outer masts 13A so as to be movable up and
down relative to the vehicle frame 12. A lift cylinder 14 as the
hydraulic mechanism is fixedly mounted in parallel relation to the
rear side of each of the outer masts 13A. Each lift cylinder 14 has
a piston rod 14A the end of which is coupled to an upper part of
the inner mast 13B.
A lift bracket 15 is mounted inward of the inner masts 13B so as to
be movable up and down along the inner masts 13B. A pair of forks
16 is mounted to the lift bracket 15. Each inner mast 13B supports
at the top thereof a chain wheel 17 around which a chain 18 is
mounted with one end thereof coupled to the lift cylinder 14 and
the other end thereof coupled to the lift bracket 15. The extending
and retracting motion of the lift cylinders 14 lifts and lowers the
lift bracket 15 and hence the forks 16 via the chains 18. In the
first embodiment, the lift cylinders 14 function as the first
hydraulic cylinder of the present invention that lifts and lowers
the forks 16.
The vehicle frame 12 has on the right and left sides thereof a pair
of hydraulically-operated tilt cylinders 19 as the hydraulic
mechanism. The tilt cylinders 19 are pivotably mounted at the base
end thereof to the vehicle frame 12. Each tilt cylinder 19 has a
piston rod 19A that is pivotably connected to the outer mast 13A in
the middle in the vertical direction of the outer mast 13A. The
extending and retracting motion of the tilt cylinders 19 causes the
mast assembly 13 to tilt forward and rearward. Specifically, the
extending and retracting motion of the tilt cylinders 19 causes the
mast assembly 13 to tilt between a predetermined frontmost tilt
position and a predetermined rearmost tilt position. With the
upright position of the mast assembly 13 shown in FIG. 1 as the
center, the movement of the mast assembly 13 tilting toward the
operator's compartment 20 corresponds to the rearward tilting
operation and the movement of the mast assembly 13 tilting away
from the operator's compartment 20 corresponds to the frontward
tilting operation, respectively. The forklift truck 11 according to
the first embodiment is so configured that the mast assembly 13 is
tilted forward and rearward by the extending and retracting
operation of the tilt cylinders 19, respectively. According to the
first embodiment, the tilt cylinders 19 function as the second
hydraulic cylinder of the present invention that tilts the mast
assembly 13, which is a hydraulically-operated unit provided
separately from the forks. The titling operation of the mast
assembly 13 corresponds to the second operation of the present
invention that is performed independently of the operation of the
forks 16.
The operator's compartment 20 includes a steering wheel 21, a lift
control lever 22, and a tilt control lever 23. In the illustration
of FIG. 1, the tilt control lever 23 is hidden by the lift control
lever 22, so that the tilt control lever 23 is not shown in the
drawing. The lift control lever 22 is operated to extend and
retract the lift cylinders 14 to thereby lift and lower the forks
16. According to the first embodiment, the lift control lever 22
functions as the first instruction member of the present invention
that instructs the lifting and lowering operation of the forks 16.
The tilt control lever 23 is operated to extend and retract the
tilt cylinders 19 to thereby tilt the mast assembly 13 forward and
rearward. According to the first embodiment, the tilt control lever
23 functions as the tilting operation instruction member that
instructs the tilting operation of the mast assembly 13. The tilt
control lever 23 is an example of the second instruction member of
the present invention that instructs the second operation that is
performed independently of the operation of the forks 16.
In the case of the forklift truck 11 having a
hydraulically-operated unit, a pair of unit hydraulic cylinders 25
as the hydraulic mechanism for operating the unit is provided to
the forklift truck 11. An example of the unit includes one that
causes the forks 16 to move right and left, tilt forward and
rearward, or rotate. In such a case, the operator's compartment 20
is provided with a unit control lever 45 that instructs the motion
of the unit. According to the first embodiment, the unit hydraulic
cylinders 25 function as the second hydraulic cylinder of the
present invention that operates the unit independently of the lift
cylinders 14 for the forks 16. Further, according to the first
embodiment, the unit control lever 45 functions as the unit
operation instruction member that instructs the operation of the
unit. The unit control lever 45 is an example of the second
instruction member that instructs the second operation that is
performed independently of the operation of the forks 16. The
operation of the unit that is performed independently of the
operation of the forks 16 corresponds to the second operation of
the present invention.
The hydraulic control device according to the first embodiment will
now be described with reference to FIG. 3. The hydraulic control
device of the first embodiment controls the operations of the lift
cylinders 14, the tilt cylinders 19 and the unit hydraulic
cylinders 25 for the loading unit. The hydraulic control device
forms a hydraulic circuit that includes a plurality of hydraulic
cylinders, a single electric motor and a single hydraulic pump that
is connected to and driven by the electric motor to operate the
hydraulic cylinders.
Each lift cylinder 14 has a bottom chamber 14B and a pipe K1 is
connected at one end thereof to the bottom chamber 14B and at the
other end thereof to a hydraulic pump motor 30 that functions as a
hydraulic pump and a hydraulic motor. An electric motor (or an
electric rotating machine) 31 that functions as an electric motor
and a generator is connected to the hydraulic pump motor 30.
According to the first embodiment, the electric motor 31 functions
as an electric motor when the electric motor 31 drives the
hydraulic pump motor 30 as a hydraulic pump, and functions as a
generator when the electric motor 31 drives the hydraulic pump
motor 30 as a hydraulic motor. The hydraulic pump motor 30
according to the first embodiment is rotatable in one
direction.
A lowering proportional valve 32 is disposed in the pipe K1 between
the lift cylinder 14 and the hydraulic pump motor 30. The lowering
proportional valve 32 according to the first embodiment is a
solenoid proportional valve. The lowering proportional valve 32 is
switchable between a first position 32A as open and a second
position 32B as closed. When the lowering proportional valve 32 is
at the first position 32A or an open position, hydraulic oil that
is discharged from the bottom chamber 14B in the lowering operation
of the forks 16 is allowed to flow to the hydraulic pump motor 30.
The opening of the lowering proportional valve 32 at the first
position 32A is variable. When the lowering proportional valve 32
is at the second position 32B, that is, when the lowering
proportional valve 32 is closed, the hydraulic oil is not allowed
to flow. The lowering proportional valve 32 of the first embodiment
corresponds to the lowering control valve of the present invention
that allows flow of the hydraulic oil from the bottom chamber 14B
of the lift cylinder 14 toward the hydraulic pump motor 30 when at
the first position 32A and that blocks flow of the hydraulic oil
from the bottom chamber 14B toward the hydraulic pump motor 30 when
at the second position. The pipe K1 in which the lowering
proportional valve 32 is disposed and which is connected between
the lift cylinder 14 and the hydraulic pump motor 30 at an intake
port 30A thereof corresponds to the lowering control valve of the
present invention. The intake port 30A corresponds to the intake
portion of the present invention. An oil tank 34 that stores
therein hydraulic oil is connected to the intake port 30A of the
hydraulic pump motor 30 through a check valve 33. The check valve
33 is configured to allow flow of the hydraulic oil from the oil
tank 34 toward the hydraulic pump motor 30 but block flow of the
hydraulic oil in the reverse direction thereof.
A pipe K2 is branched from the pipe K1 at a position between the
lowering proportional valve 32 and the hydraulic pump motor 30
connected to the oil tank 34 on the downstream side of the lowering
proportional valve 32. The pipe K2 corresponds to the drain passage
(or the bypass passage) of the present invention. A flow rate
control valve 35 is disposed in the pipe K2 and controls the flow
rate of the hydraulic oil flowing in the pipe K2. The flow rate
control valve 35 is switchable among a first position 35A as open,
a second position 35B as closed, and a third position 35C also as
open. The opening of the flow rate control valve 35 at the third
position 35C is variable. The flow rate control valve 35 according
to the first embodiment is configured to be switchable to any one
of the first position 35A, the second position 35B, and the third
position 35C according to a difference between a pressure P1 in the
pipe between the lift cylinder 14 and the lowering proportional
valve 32 and a pressure P2 in the pipe between the lowering
proportional valve 32 and the hydraulic pump motor 30.
When the lowering proportional valve 32 is at the second position
32B and the lowering operation of the forks 16 is not performed,
the pressure P1 is larger than the pressure P2. According to the
pressure difference between the pressure P1 and the pressure P2,
the flow rate control valve 35 is switched to the closed position
(or the second position 35B). When the lowering proportional valve
32 is switched to the open position (or the first position 32A) to
allow the hydraulic oil to flow therethrough, the pressure
difference between the pressure P1 and the pressure P2 decreases to
thereby switch the lowering proportional valve 32 to the open
position (the third position 35C or the first position 35A). At
this time, the opening of the flow rate control valve 35 is
decreased as the pressure difference between the pressure P1 and
the pressure P2 increases and is increased as the pressure
difference between the pressure P1 and the pressure P2 decreases.
Also, the hydraulic oil is allowed to flow toward the hydraulic
pump motor 30 through the pipe K1 at a flow rate Q1 shown in FIG.
3, and the hydraulic oil is allowed to flow through the pipe K2 to
return to the oil tank 34 (or the return side) at a flow rate that
is determined according to the opening of the flow rate control
valve 35. When the pressure difference between the pressure P1 and
the pressure P2 increases at a later time with an increase of the
rotation speed of the hydraulic pump motor 30, the flow rate
control valve 35 is switched to the closed position again. At this
time, the hydraulic oil is allowed to flow toward the hydraulic
pump motor 30 only through the pipe K1 at the flow rate Q1 shown in
FIG. 3. Specifically, when the flow rate control valve 35 is
switched to the second position 35B, the hydraulic oil that is
discharged from the bottom chamber 14B of the lift cylinder 14 is
allowed to flow through the lowering proportional valve 32 into the
hydraulic pump motor 30 through its intake port 30A. In this case,
the whole of the hydraulic oil that has flowed through the lowering
proportional valve 32 is flowed into the hydraulic pump motor 30
through the intake port 30A at the flow rate Q1. When the flow rate
control valve 35 is switched to either the first position 35A or
the third position 35C, on the other hand, the hydraulic oil that
is discharged from the bottom chamber 14B of the lift cylinder 14
is allowed to flow through the lowering proportional valve 32 into
the hydraulic pump motor 30 the intake port 30A and also to the oil
tank 34. In this case, a part of the hydraulic oil that has flowed
through the lowering proportional valve 32 is flowed to the
hydraulic pump motor 30 through the intake port 30A at the flow
rate Q1 shown in FIG. 3, and the remaining part of the hydraulic
oil is flowed to the oil tank 34 at a flow rate Q2 shown in FIG. 3.
The flow rate control valve 35 is configured to open at a desired
opening in accordance with the pressure difference.
A lifting proportional valve 37 is connected to a portion of the
pipe K1 that extends from a discharge port 30B of the hydraulic
pump motor 30. The lifting proportional valve 37 is switchable
between a first position 37A as open and a second position 37B as
closed. When the lifting proportional valve 37 is at the first
position 37A or an open position, hydraulic oil that is discharged
from the hydraulic pump motor 30 is allowed to flow through a check
valve 38 to the bottom chamber 14B of the lift cylinder 14. The
opening of the lifting proportional valve 37 at the first position
37A is variable. When the lifting proportional valve 37 is at the
second position 37B, that is, when the lifting proportional valve
37 is closed, the hydraulic oil is allowed to flow toward a tilting
proportional valve 39 that is connected to a pipe K3. The check
valve 38 is configured to allow the flow of the hydraulic oil that
has passed through the lifting proportional valve 37 toward the
bottom chamber 14B of the lift cylinder 14 but block the flow of
the hydraulic oil in the reverse direction thereof, that is, from
the bottom chamber 14B of the lift cylinder 14 toward the lifting
proportional valve 37.
A pipe K4 is branched from the pipe K1 on the discharge port 30B
side of the hydraulic pump motor 30 and connected to the oil tank
34 through a filter 40, and a pipe K5 is branched from the pipe K1
and connected to the tilting proportional valve 39. A relief valve
41 for preventing an excessive increase of pressure of the
hydraulic oil is connected to the pipe K4. A pipe K6 is connected
to the pipe K4 and allows the hydraulic oil that has passed through
the tilting proportional valve 39 to flow toward the oil tank 34. A
check valve 42 is provided in the pipe K5. The check valve 42 is
configured to allow flow of the hydraulic oil from the hydraulic
pump motor 30 toward the tilting proportional valve 39 but block
flow of the hydraulic oil in the reverse direction thereof, that
is, from the tilting proportional valve 39 to the hydraulic pump
motor 30.
The tilting proportional valve 39 is switchable among a first
position 39A as closed, a second position 39B as open, and a third
position 39C as open. The opening of the tilting proportional valve
39 at the second and third positions 39B, 39C is variable. When the
tilting proportional valve 39 is at the first position 39A, the
hydraulic oil that has passed through the lifting proportional
valve 37 in the pipe K3 is allowed to flow to the oil tank 34. The
tilting proportional valve 39 according to the first embodiment is
normally placed the first position 39A as the neutral position and
switched to either the second position 39B or the third position
39C according to the control by a controller S. When the tilting
proportional valve 39 is at the second position 39B, the hydraulic
oil that has passed through the check valve 42 is allowed to flow
through a pipe K7 that is connected to a rod chamber 19R of the
tilt cylinder 19. Further, when the tilting proportional valve 39
is at the second position 39B, the hydraulic oil that is discharged
from a bottom chamber 19B of the tilt cylinder 19 is allowed to
flow through the pipe K6. When the tilting proportional valve 39 is
at the third position 39C, the hydraulic oil that has passed
through the check valve 42 is allowed to flow through a pipe K8 and
the hydraulic oil that is discharged from the rod chamber 19R of
the tilt cylinder 19 and flows through the pipe K7 is allowed to
flow through the pipe K6.
A unit proportional valve 43 is connected in the pipe K3 between
the tilting proportional valve 39 and the oil tank 34. A pipe K9 is
connected the pipe K4 and allows flow of the hydraulic oil from the
unit proportional valve 43 flows to the oil tank 34. The pipe K5 is
connected to the unit proportional valve 43. A check valve 44 is
provided in the pipe K5 and allows flow of the hydraulic oil from
the hydraulic pump motor 30 toward the unit proportional valve 43
but blocks flow of the hydraulic oil from the unit proportional
valve 43 toward the hydraulic pump motor 30.
The unit proportional valve 43 is switchable among a first position
43A as closed, a second position 43B as open, and a third position
43C as open. The opening of the unit proportional valve 43 at the
second and third positions 43B, 43C is variable. When the unit
proportional valve 43 is at the first position 43A, the hydraulic
oil that has passed through the tilting proportional valve 39
through the pipe K3 is allowed to flow to the oil tank 34. The unit
proportional valve 43 according to the first embodiment is normally
placed in the first position 43A as the neutral position and
switched to either the second position 43B or the third position
43C according to the control by the controller S. When the unit
proportional valve 43 is at the second position 43B, the hydraulic
oil that has passed through the check valve 44 is allowed to flow
through a pipe K10 that is connected to a rod chamber 25R of the
unit hydraulic cylinder 25 for unit. When the unit proportional
valve 43 is at the second position 43B, the hydraulic oil that is
discharged from a bottom chamber 25B of the unit hydraulic cylinder
25 and flows through a pipe K11 is allowed to flow through the pipe
K9. When the unit proportional valve 43 is at the third position
43C, the hydraulic oil that has passed through the check valve 44
is allowed to flow through the pipe K11 and the hydraulic oil that
is discharged from the rod chamber 25R of the unit hydraulic
cylinder 25 is allowed to flow in the pipe K10 is allowed to flow
through the pipe K9.
The controller S of the hydraulic control device will now be
described with reference to FIG. 3.
The controller S includes a potentiometer 22A that detects the
operation amount of the lift control lever 22, a potentiometer 23A
that detects the operation amount of the tilt control lever 23, and
a potentiometer 45A that detects the operation amount of the unit
control lever 45 that are all electrically connected to the
controller S. The controller S controls the rotation of the
electric motor 31 and the switching of the lowering proportional
valve 32 and the lifting proportional valve 37, in response to
detection signal from the potentiometer 22A based on the detected
operation amount of the lift control lever 22. The controller S
controls the rotation of the electric motor 31 and the switching of
the tilting proportional valve 39, in response to detection signal
from the potentiometer 23A based on a detected operation amount of
the tilt control lever 23. The controller S controls the rotation
of the electric motor 31 and the switching of the unit proportional
valve 43, in response to detection signal from the potentiometer
45A based on a detected operation amount of the unit control lever
45.
An inverter S1 is electrically connected to the controller S and
the power from a battery BT is supplied to the electric motor 31
through the inverter S1. The power generated by the electric motor
31 is stored in the battery BT through the inverter S1.
The operation of the hydraulic control device according to the
first embodiment will now be described with reference to FIG.
2.
Referring to FIG. 2 showing a relationship among the opening of the
lowering proportional valve 32, the rotation speed of the hydraulic
pump motor 30, and the flow rate of the hydraulic oil that is
discharged from the lift cylinder 14 in the hydraulic control
device according to the first embodiment, the dotted region
corresponds to the flow rate Q1 of the hydraulic oil flowing toward
the hydraulic pump motor 30, and the blank region corresponds to
the flow rate Q2 at which the hydraulic oil is flowed toward the
flow rate control valve 35.
As shown in FIG. 2, in the hydraulic control device according to
the first embodiment, the flow rate of the hydraulic oil discharged
from the lift cylinder 14 increases with an increase of the opening
of the lowering proportional valve 32. The hydraulic oil discharged
from the lift cylinder 14 is divided into two ways, namely one
flowing at the flow rate Q1 toward the intake port 30A of the
hydraulic pump motor 30 and the other flowing at the flow rate Q2
toward the flow rate control valve 35, according to the rotation
speed of the hydraulic pump motor 30. Specifically, as shown in
FIG. 2, the hydraulic oil that is discharged from the lift cylinder
14 flows at a higher flow rate toward the flow rate control valve
35 with a decrease of the rotation speed of the hydraulic pump
motor 30.
The hydraulic pump motor 30 operating at a low rotation speed does
not take in sufficient amount of the hydraulic oil from the lift
cylinder 14. Therefore, the pressure difference between the
pressure P1 and the pressure P2, that is, the difference between
the pressures of hydraulic oil before and after passing through the
lowering proportional valve 32 is decreased and the opening of the
flow rate control valve 35 is increased. As a result, as shown in
FIG. 2, the hydraulic oil flows from the lift cylinder 14 at a
higher flow rate toward the flow rate control valve 35 with a
decrease of the rotation speed of the hydraulic pump motor 30. On
the other hand, when the rotation speed of the hydraulic pump motor
30 is increased, the hydraulic pump motor 30 takes in a larger
amount of hydraulic oil. Therefore, the pressure difference between
the pressure P1 and the pressure P2, that is, the difference
between the pressures of hydraulic oil before and after passing
through the lowering proportional valve 32 is increased and the
opening of the flow rate control valve 35 is decreased. As a
result, as shown in FIG. 2, the hydraulic oil flows from the lift
cylinder 14 at a higher flow rate toward the hydraulic pump motor
30 with an increase of the rotation speed of the hydraulic pump
motor 30.
The flow rates Q1 and Q2 are thus controlled in the hydraulic
control device. The following will describe the control performed
by the hydraulic control device according to the first embodiment
of the present invention when the lowering operation of the forks
16 is performed simultaneously with another operation that is
different from the lowering operation of the forks 16, which may be
referred herein to as a second operation. It is to be noted that
the second operation of the forklift truck 11 according to the
first embodiment corresponds to the tilting operation of the mast
assembly 13 or to any operation associated with the unit. In the
case that the tilting operation of the mast assembly 13 is
performed simultaneously with the lowering operation of the forks
16, the second operation is either the forward tilting operation or
the rearward tilting operation of the mast assembly 13. In the case
that the operation associated with the unit is performed
simultaneously with the lowering operation of the forks 16 and if
the unit is configured to make a single motion, the single motion
or operation corresponds to the second operation, and if the unit
is configured to make a plurality of different motions, one of the
multiple operations corresponds to the second operation.
The control of the hydraulic control device will now be described
with reference to FIGS. 4A to 4C. It is to be noted that the
description of the control herein is applicable to any operation
that may be performed simultaneously with the lowering operation of
the forks 16. Therefore, for the ease of description, the second
operation that is performed simultaneously with the lowering
operation of the forks 16 will not be specified in the description
below.
FIG. 4A shows the operation amount of the lift control lever 22
(hereinafter, the lift operation amount) and the operation amount
of the control lever that instructs the second operation
(hereinafter, the second operation amount). Solid line L1 in FIG.
4A shows the lift operation amount and solid line L2 shows the
second operation amount. In the example shown in FIG. 4A, the
lowering operation of the forks 16 is performed during a period
between time t0 and time t2, and the second operation is performed
during a period between time t1 and time t3. As shown in FIG. 4A,
the lowering operation of the forks 16 and the second operation are
performed simultaneously during a period between the time t1 and
the time t2.
FIG. 4B shows the rotation speed of the hydraulic pump motor 30
when the control levers are operated in the manner as indicated in
FIG. 4A. R1 in FIG. 4B represents the rotation speed of the
hydraulic pump motor 30 that is required for operating the forks 16
at the instruction speed corresponding to the lift operation amount
(hereinafter, the required lift operation rotation speed). R2
represents the rotation speed of the hydraulic pump motor 30 that
is required for performing the second operation at the instruction
speed corresponding to the second operation amount (hereinafter,
the required second operation rotation speed). Solid line Rx
represents the actual rotation speed of the hydraulic pump motor 30
during the operation of the hydraulic control device according to
the first embodiment. In the example shown in FIG. 4B, R2
corresponds to the required second operation rotation speed and R1
corresponds to the required lift operation rotation speed, where R2
is higher than R1.
Under the conditions above, the controller S calculates the
required lift operation rotation speed based on the lift operation
amount for the period between the time t0 and the time t1 during
which the lowering operation of the forks 16 is solely performed
and also calculates the opening of the lowering proportional valve
32. Then, the controller S controls the instruction rotation speed
of the electric motor 31 so as to operate the hydraulic pump motor
30 at the required lift operation rotation speed. Further, the
controller S opens the lowering proportional valve 32 at the first
position 32A at the calculated opening. When the lowering operation
of the forks 16 is performed solely without the second operation,
that is, when the forklift truck is in a single operation mode, the
controller S places the lifting proportional valve 37 at the second
position 37B, the tilting proportional valve 39 at the first
position 39A, and the unit proportional valve 43 at the first
position 43A, respectively.
When the lowering proportional valve 32 is opened, the hydraulic
oil discharged from the bottom chamber 14B of the lift cylinder 14
flows toward the hydraulic pump motor 30 through the lowering
proportional valve 32. When the hydraulic pump motor 30 is driven
by the hydraulic oil discharged from the bottom chamber 14B at a
rotation speed that is high enough to achieve the instructed speed,
the output torque of the electric motor 31 becomes a negative
value. Then the electric motor 31 performs a regenerative
operation. Specifically, the hydraulic pump motor 30 functions as a
hydraulic motor and, accordingly, the electric motor 31 being
driven by the hydraulic pump motor 30 functions as a generator. The
power thus generated by the electric motor 31 then operating as a
generator is stored in the battery BT.
The control lever for the second operation is moved or operated at
the time t1 and, accordingly, simultaneous operation in which the
lowering operation of the forks 16 and the second operation are
performed simultaneously begins. Detecting such operation of the
control lever for the second operation, the controller S calculates
the required second operation rotation speed based on the second
operation amount and then controls the instruction rotation speed
of the electric motor 31 so as to operate the hydraulic pump motor
30 at the calculated speed. Specifically, during the simultaneous
operation, the controller S causes the hydraulic pump motor 30 to
operate at the rotation speed R2 that corresponds to the required
second operation rotation speed.
A case will be considered in which the required second operation
rotation speed is higher than the required lift operation rotation
speed as indicated by dash-dot line in FIG. 4B.
As shown in FIG. 1, the hydraulic control device according to the
first embodiment has a single hydraulic pump motor 30. Further, as
shown in FIG. 2, providing that the opening of the lowering
proportional valve 32 is fixed, the flow rate of the hydraulic oil
discharged from the lift cylinder 14 increases with an increase of
the rotation speed of the hydraulic pump motor 30. Referring to
FIG. 4C, a speed V1 represents a speed of the lowering operation of
the forks 16 when the hydraulic pump motor 30 is operated at a
rotation speed corresponding to the required lift operation
rotation speed during the period between the time t0 and the time
t1. The speed V1 rises as indicated by a chain double-dashed line
W1 in FIG. 4C, with an increase of the rotation speed of the
hydraulic pump motor 30 to a rotation speed corresponding to the
required second operation speed. Specifically, with an increase of
the operation speed due to an increase in the flow rate of the
hydraulic oil discharged from the lift cylinder 14, the lowering
operation of the forks 16 is supposed to be performed at the
instruction speed (at the speed V1) or higher.
In the case that the lowering operation of the forks 16 and the
second operation are performed simultaneously on the conditions
described above, the hydraulic control device according to the
first embodiment sets the upper limit rotation speed of the
hydraulic pump motor 30 so as to restrict an excessive increase in
the operation speed of the lowering operation of the forks 16.
According to the first embodiment, the controller S sets the
rotation speed R1 shown in FIG. 4B and corresponding to the
required lift operation rotation speed as the upper limit rotation
speed. The rotation speed R1 corresponds to the required lift
operation rotation speed that is required for the lowering
operation of the forks 16 at the instruction speed that is based on
the lift operation amount at the time when the simultaneous
operation mode is started. When the rotation speed of the hydraulic
pump motor 30 is higher than the upper limit rotation speed (the
rotation speed R1), the controller S controls the instruction
rotation speed of the electric motor 31 so as to restrict the
operation of the hydraulic pump motor 30. At this time, the
instruction rotation speed of the electric motor 31 corresponds to
the rotation speed for operating the hydraulic pump motor 30 at the
upper limit rotation speed (the rotation speed R1 corresponding to
the required lift operation rotation speed). Accordingly, as shown
in FIG. 4B, the rotation speed of the hydraulic pump motor 30 is
restricted to the rotation speed R1 that corresponds to the
required lift operation rotation speed without being increased to
the rotation speed R2 that corresponds to the required second
operation rotation speed. As a result, as shown in FIG. 4C, the
operation speed of the lowering operation of the forks 16 is
controlled to the speed V1 during the period between the time t1
and the time t2 during which the lowering operation and the second
operation are performed simultaneously. Meanwhile, as indicated by
the thick line in FIG. 4C, the operation speed of the second
operation is restricted to an operation speed that is lower than
the instruction speed (the speed V2 in FIG. 4C) because the
rotation speed of the hydraulic pump motor 30 is restricted to the
upper limit rotation speed (the rotation speed R1). In other words,
the operation speed of the second operation may be an operation
speed (the speed V1) according to the upper limit rotation
speed.
When the lowering operation of the forks 16 is finished at the time
t2, that is, by returning the lift control lever 22 to the neutral
position, the second operation may be performed solely in the
single operation mode. It is supposed that in this case the
controller S controls the operation of the hydraulic pump motor 30
at the required second operation rotation speed so as to achieve
the instruction speed of the second operation, without controlling
the hydraulic pump motor 30 to prevent the hydraulic pump motor 30
from operating beyond the upper limit operation speed. In this
case, the operation speed of the second operation is supposed to
increase as indicated by a chain double-dashed line W2 in FIG. 4C
with an increase of the rotation speed of the hydraulic pump motor
30 after the time t2 as indicated by the chain double-dashed line Y
in FIG. 4B.
Even after the operation is changed from the simultaneous operation
mode in which the lowering operation of the forks 16 and the second
operation are performed simultaneously to the single operation mode
in which the second operation is solely performed, the hydraulic
control device according to the first embodiment continues the
restriction of the rotation speed of the hydraulic pump motor 30
for the upper limit rotation speed that is used in the
afore-mentioned simultaneous operation mode in which two operations
are performed simultaneously. Specifically, the controller S
continues the restriction of the rotation speed of the hydraulic
pump motor 30 during the period between the time t2 and the time t3
at which the second operation is finished. Therefore, the rotation
speed of the hydraulic pump motor 30 is maintained at the upper
limit rotation speed (or the rotation speed R1) after the time t2,
as shown in FIG. 4B, with the result that the operation speed of
the second operation may be at the speed V1 that corresponds to the
upper limit rotation speed.
It is to be noted that the upper limit rotation speed according to
the first embodiment corresponds to the required lift operation
rotation speed, so that the upper limit rotation speed increases to
a rotation speed Ra in FIG. 4B, for example, with an increase of
the lift operation amount to La in FIG. 4A. Specifically, as the
lift operation amount is increased from the example of FIG. 4A, the
operation speed of the second operation that is performed
simultaneously with the lowering operation of the forks 16 is
increased, approaching the speed V2.
In the first embodiment, the upper limit rotation speed varies
according to the instruction speed of the lowering operation of the
forks 16 based on the lift operation amount. Such variation of the
upper limit rotation speed remains valid when the instruction speed
of the lowering operation of the forks 16 increases in accordance
with the increase in the lift operation amount during the
simultaneous operation of the lowering operation of the forks 16
and the second operation. Therefore, when the lift operation amount
is increased during the simultaneous operation mode, the operation
speed of the lowering operation of the forks 16 increases, and the
operation speed of the second operation also increases with an
increase in the upper limit rotation speed. Specifically, during
the simultaneous operation mode, when the required lift operation
rotation speed exceeds the upper limit rotation speed that is set
at the start of the simultaneous operation mode in which the two
operations are simultaneously performed in response to the increase
in the lift operation amount, then the upper limit rotation speed
is changed to a higher rotation speed in accordance with the
increase of the required lift operation rotation speed.
It is to be noted that, in the case that the required lift
operation rotation speed is higher than the required second
operation rotation speed, the flow rate control valve 35 of the
hydraulic control device according to the first embodiment achieves
the operation speed of the lowering operation of the forks 16. As
described above, the hydraulic control device according to the
first embodiment determines the rotation speed of the hydraulic
pump motor 30 as the required second operation rotation speed, so
that when the required second operation rotation speed is low, the
hydraulic oil discharged from the lift cylinder 14 is hard to be
taken into the hydraulic pump motor 30. In such case, however, the
pressure difference between the pressure P1 and the pressure P2,
that is, the difference between the pressures before and after
passing through the lowering proportional valve 32, respectively,
is decreased and, accordingly, the opening of the flow rate control
valve 35 is increased. As a result, the hydraulic oil discharged
from the lift cylinder 14 is allowed to flow through the drain
passage (or the pipe K2) shown in FIG. 3, and the operation speed
of the lowering operation of the forks 16 is achieved.
In the hydraulic control device according to the first embodiment,
in the case that the required lift operation rotation speed, which
may be the upper limit rotation speed, is the required second
operation rotation speed or higher, that is, in the case that the
required second operation rotation speed is the required lift
operation rotation speed or lower, the controller S does not
restrict the rotation speed of the hydraulic pump motor 30 by the
upper limit rotation speed. Specifically, in the above case, the
controller S controls the instruction rotation speed of the
electric motor 31 so as to operate the hydraulic pump motor 30 at
the required second operation rotation speed.
The first embodiment of the present invention offers the following
effects.
(1) In the case that the lowering operation of the forks 16 and the
second operation are performed simultaneously, an abrupt change of
the operation speed of the lowering operation of the forks 16 may
be prevented by restricting the rotation speed of the hydraulic
pump motor 30 to the upper limit rotation speed. On the other hand,
although the operation speed of the second operation becomes lower
with respect to the instruction speed, the change of the operation
speed of the second operation may be made smaller. Therefore, a
plurality of operations of a forklift truck may be performed
successfully.
(2) According to the first embodiment, by setting the upper limit
rotation speed to a rotation speed corresponding to the required
lift operation rotation speed, the lowering operation of the forks
16 is performed without irregular variation in the operation speed
during switching of the operation from the single operation mode of
the second operation to the simultaneous operation mode.
(3) Because the rotation speed of the hydraulic pump motor 30 is
restricted to the upper limit rotation speed, no abrupt change
occurs in the operation speed during switching of the operation
from the simultaneous operation mode to the single operation mode
of the second operation.
(4) By setting the upper limit rotation speed to a rotation speed
corresponding to the required lift operation rotation speed, the
upper limit rotation speed may be changed in accordance with the
change in the lift operation amount. Specifically, by changing the
upper limit rotation speed, the operation speed of the lowering
operation of the forks 16 may be increased in accordance with the
increasing instruction speed, and the operation speed of the second
operation may be increased, accordingly. As a result, a plurality
of loading operations is operated in a preferred manner.
Second Embodiment
A hydraulic control device of a forklift truck according to a
second embodiment of the present invention will now be described
with reference to FIGS. 5A to 5C. In the following description, the
configuration and the control that have already been mentioned in
the description of the first embodiment will be simplified or not
be reiterated.
The second embodiment is different from the first embodiment in the
rotation speed set as the upper limit rotation speed that restricts
the rotation speed of the hydraulic pump motor 30, but the first
and second embodiments are substantially the same in other respects
including the control.
FIG. 5A is similar to FIG. 4A and shows the lift operation amount
and the second operation amount. FIG. 5B is similar to FIG. 4B and
shows the rotation speed of the hydraulic pump motor 30 when the
control levers are operated. A rotation speed R1 corresponds to the
required lift operation rotation speed and a rotation speed R2
corresponds to the required second operation rotation speed of the
hydraulic pump motor 30, respectively. A rotation speed Rx is the
actual rotation speed of the hydraulic pump motor 30 when the
lowering operation of the forks 16 and the second operation are
performed simultaneously by the hydraulic control device.
The upper limit rotation speed according to the second embodiment
is set at the rotation speed Rx that is lower than the rotation
speed required for operating the hydraulic part of the forklift
truck 11 (e.g. the mast assembly 13 and the unit) at the highest
instruction speed that is based on the operation of the control
lever for the second operation. It is to be noted that the upper
limit rotation speed according to the second embodiment is
fixed.
When the lowering operation of the forks 16 and the second
operation are performed simultaneously at the time t1, the
controller S calculates the required second operation rotation
speed based on the second operation amount. The controller S then
controls the instruction rotation speed of the electric motor 31 so
as to operate the hydraulic pump motor 30 at the calculated
required second operation rotation speed. Specifically, in the
simultaneous operation of the lowering operation and the second
operation, the controller S causes the hydraulic pump motor 30 to
operate at the rotation speed R2 corresponding to the required
second operation rotation speed.
Subsequently, in the state where the required second operation
rotation speed is higher than the required lift operation rotation
speed, the controller S determines whether or not the required lift
operation rotation speed is higher than the rotation speed Rx that
corresponds to the upper limit rotation speed. When the required
lift operation rotation speed is lower than the rotation speed Rx,
then the controller S restricts the operation of the hydraulic pump
motor 30. When the required second operation rotation speed that
corresponds to the required rotation speed of the hydraulic pump
motor 30 is higher than the upper limit rotation speed (or the
rotation speed Rx), then the controller S restricts the rotation
speed of the hydraulic pump motor 30 to the upper limit rotation
speed. In response to the control, the rotation speed of the
hydraulic pump motor 30 is restricted to the rotation speed Rx that
corresponds to the upper limit rotation speed, as shown in FIG. 5B,
without being raised to the rotation speed R2 corresponding to the
required second operation rotation speed. As a result, as shown in
FIG. 5C, the operation speed of the lowering operation of the forks
16 is controlled to the speed Vx in the period between t1 and t2
during which the lowering operation of the forks 16 and the second
operation are performed simultaneously. The speed Vx is higher than
the speed V1 that corresponds to the required lift operation
rotation speed but lower than the speed V2 that corresponds to the
required second operation rotation speed. Meanwhile, by restricting
the rotation speed of the hydraulic pump motor 30 to the upper
limit rotation speed (the rotation speed Rx), the hydraulic pump
motor 30 for the operation speed of the second operation is
restricted to the operation speed that is lower than the
instruction speed (the speed V2 in FIG. 5C) as indicated by the
thick dotted line in FIG. 5C. However, the operation speed of the
second operation is higher than the speed V1 that corresponds to
the instruction speed for the lowering operation of the forks 16
and approximate to the speed V2 that corresponds to the instruction
speed for the second operation.
As in the case of the first embodiment, even after the operation is
changed from the simultaneous operation mode in which the lowering
operation of the forks 16 and the second operation are performed
simultaneously to the single operation mode in which the second
operation is solely performed, the controller S continues the
restriction of the rotation speed of the hydraulic pump motor 30 to
the upper limit rotation speed that is used in the afore-mentioned
simultaneous operation mode. Specifically, the controller S
continues the restriction of the rotation speed of the hydraulic
pump motor 30 during the period between the time t2 and the time t3
at which the second operation is finished. As shown in FIG. 5B, the
rotation speed of the hydraulic pump motor 30 is maintained at the
upper limit rotation speed (the rotation speed Rx) after the time
t2 and, therefore, the operation speed of the second operation may
be the speed Vx corresponding to the upper limit rotation
speed.
It is to be noted that the upper limit rotation speed according to
the second embodiment is a fixed rotation speed, so that, when the
required lift operation rotation speed is higher than the rotation
speed Rx which is the upper limit rotation speed, the controller S
does not restrict the instruction rotation speed of the electric
motor 31 with the upper limit rotation speed. This is because, if
the instruction rotation speed is restricted when the required lift
operation rotation speed is higher than the upper limit rotation
seed, the operation speed of the lowering operation of the forks 16
will also be decreased. Therefore, when the required lift operation
rotation speed is higher than the upper limit rotation speed, the
controller S controls the instruction rotation speed of the
electric motor 31 so that the rotation speed of the hydraulic pump
motor 30 becomes the required second operation rotation speed (the
rotation speed R2 in FIG. 5B). Further, according to the second
embodiment, when the upper limit rotation speed is higher than the
required second operation rotation speed, that is, when the
required second operation rotation speed is the upper limit
rotation speed or lower, the controller S does not restrict the
rotation speed of the hydraulic pump motor 30 with the upper limit
rotation speed. Specifically, in the above case, the controller S
controls the instruction rotation speed of the electric motor 31 so
as to operate the hydraulic pump motor 30 at the required second
operation rotation speed.
It is to be noted that the upper limit rotation speed according to
the second embodiment may be determined based on one specific
second operation of plural second operations. For example, the
specific second operation may be the tilting operation of the mast
assembly 13. Alternatively, the upper limit rotation speed
according to the second embodiment may be determined individually
for each different second operation. In this case, the controller S
sets the upper limit rotation speed for each of the second
operations that are performed simultaneously with the lowering
operation of the forks 16. In the case that the lowering operation
of the forks 16 and any two or more second operations are performed
simultaneously, the controller S may designate the upper limit
rotation speed according to any one selected second operation. For
example, the selected one of the second operations may be the
second operation the required rotation speed of which is the
highest.
According to the second embodiment, by restricting the rotation
speed of the hydraulic pump motor 30 to the upper limit rotation
speed, as described earlier, the operation speed of the lowering
operation of the forks 16 becomes higher than the instructed speed.
Therefore, it is preferable that the upper limit rotation speed
should be set only to such an extent that causes no abrupt change
in the operation speed and such speed may be found through
simulations or the like.
The second embodiment offers the following effects in addition to
the effect described under (1) with reference to the first
embodiment.
(5) When the loading operation of the forklift truck is changed
from the simultaneous operation mode in which the lowering
operation of the forks 16 and the second operation are
simultaneously performed to the single operation mode in which the
second operation is solely performed, the rotation speed of the
hydraulic pump motor 30 is restricted to the upper limit rotation
speed and, therefore, the operation speed of the second operation
is prevented from being changed abruptly.
(6) When the required lift operation rotation speed that is the
upper limit rotation speed or higher, the operation speeds of the
respective operations are not restricted, so that the operations
may be performed smoothly. It is to be noted that the above first
and second embodiments may variously be modified as described
below.
In the above embodiments, the rotation speed of the hydraulic pump
motor 30 may not be restricted when the lift operation amount is
small. In this case, the controller S controls the instruction
rotation speed of the electric motor 31 so as to operate the
hydraulic pump motor 30 at the required second operation rotation
speed, so that the second operation is performed at the instruction
speed that is required by the second operation amount. When the
lift operation amount is small, the required lift operation
rotation speed is small and the opening of the lowering
proportional valve 32 is also small. As shown in FIG. 2, when the
opening of the lowering proportional valve 32 is small, the
hydraulic oil that is required for the second operation is taken in
by the hydraulic pump motor 30 from the oil tank 34, without being
influenced by the rotation speed of the hydraulic pump motor 30. In
other words, the hydraulic oil discharged from the lift cylinder 14
is not taken in easily by the hydraulic pump motor 30. When the
opening of the lowering proportional valve 32 is small, the
operation speed of the lowering operation of the forks 16 is not
affected significantly by the operation of the hydraulic pump motor
30 at the required operation speed of the second operation and
therefore, no abrupt change occurs in the operation speed of the
lowering operation of the forks 16. The aforementioned small
opening of the lowering proportional valve 32 refers to the opening
of the lowering proportional valve 32 of, for example, about 30% of
the fully opened state, at which the hydraulic pump motor 30 cannot
take in the hydraulic oil on the lift cylinder 14 side. The opening
of the lowering proportional valve 32 that may be the reference for
determining whether or not the restriction should be performed by
the upper limit rotation speed, is considered to vary according to
the capacity of the hydraulic pump motor 30 and the structure of
the lowering proportional valve 32 (e.g. the diameter of the
lowering proportional valve 32 as measured at full open).
Therefore, it is preferable that the opening of the lowering
proportional valve 32 should be set through simulations or the
like, taking such factors into consideration. According to the
configuration, it is possible that various loading operations may
be accomplished without restricting their operation speed.
In the above embodiments, the hydraulic control device may be
adapted to control the lifting and lowering operation of the forks
16 and the tilting operation of the mast assembly 13. According to
such hydraulic control device, in the case that the lowering
operation of the forks 16 and at least one of the frontward tilting
operation or the rearward tilting operation are performed
simultaneously, the hydraulic control device restricts the rotation
speed of the hydraulic pump motor 30 to the upper limit rotation
speed.
In the above embodiments, the hydraulic control device may be a
hydraulic control device of a forklift truck that includes a
plurality of units and a hydraulic mechanism (a hydraulic cylinder)
that drives the plural units.
In the above embodiments, the hydraulic control device may be
adapted for use in a forklift truck that has a hydraulic power
steering mechanism as the hydraulic mechanism. The hydraulic power
steering mechanism has an independent hydraulic cylinder that
drives the steering device that is a separate
hydraulically-operated unit other than the forks 16.
In the above embodiments, in the case that two or more second
operations are performed simultaneously with the lowering operation
of the forks 16, the required rotation speed of the hydraulic pump
motor 30 may be calculated in the following manner. The controller
S calculates the required speeds of the hydraulic pump motor 30 for
the respective second operations. The controller S controls the
instruction rotation speed of the electric motor 31 so as to
operate the hydraulic pump motor 30 at the rotation speed that is
the highest of the calculated required rotation speeds for the
second operations. The controller S also restricts the rotation
speed of the hydraulic pump motor 30 to the upper limit rotation
speed as in the case of the first and second embodiments. This
configuration enables a system in which, when two or more second
operations are performed simultaneously with the lowering operation
of the forks 16, the variation in the operation speed not only of
the lowering operation but also of the operation speeds of the
second operations are made smaller. In the modified embodiment, if
the mast assembly 13 and a unit are operated simultaneously with
the lowering operation of the forks 16, the tilt cylinders 19 that
drive the mast assembly 13 and the unit hydraulic cylinders 25 that
drive the unit correspond to the plurality of hydraulic cylinders
of the present invention. The mast assembly 13 and the unit
correspond to the plurality of hydraulically-operated units of the
present invention. The instruction members that instruct the
operation of the mast assembly 13 and the unit correspond to the
plurality of instruction members. The second operation includes but
not limited to the aforementioned second operations of the mast
assembly 13 and the unit. For example, the steering operation of
the hydraulic power steering mechanism in the modified embodiment
may be the second operation. In the case that the unit handles a
plurality of operations and such operations are individually
controlled by separate hydraulic cylinders, each of the operations
of the unit may be the second operation.
According to the present invention, the instruction members that
instruct lifting operation of the forks 16, tilting operation of
the mast assembly 13, and operation of the unit may not necessarily
be of a lever type, but it includes any other type of instruction
member, such as a pushbutton switch.
According to the present invention, the control valves such as the
tilting proportional valve 39 and the unit proportional valve 43
may not necessarily be of a solenoid type, and mechanical or
hydraulic valves may also be used.
According to the present invention, the control valves such as the
lowering proportional valve 32 and the lifting proportional valve
37 may not necessarily be of a solenoid type, and mechanical or
hydraulic valves may also be used.
According to the above embodiments, the hydraulic control device
has a mechanism that allows the flow of hydraulic oil from the lift
cylinder 14 toward the hydraulic pump motor 30 during the lowering
operation of the forks 16 but blocks the flow of hydraulic oil from
the lift cylinder 14 toward the hydraulic pump motor 30 during the
lifting operation of the forks 16 or when the operation of the
forks 16 is at a stop. According to the present invention, however,
the mechanism may be modified, for example, as shown in FIG. 6. The
mechanism of FIG. 6 includes a poppet valve 51 and a solenoid valve
52 in addition to the lowering proportional valve 32. In the
lowering operation of the forks 16, the poppet valve 51 and the
solenoid valve 52 are both opened and the flow rate of the
hydraulic oil flowing toward the hydraulic pump motor 30 is
controlled by the opening of the lowering proportional valve 32.
The flow rate control valve 35 is opened in accordance with the
difference in the pressure between the pressure in the pipe between
the lift cylinder 14 and the lowering proportional valve 32 and the
pressure in the pipe between the lowering proportional valve 32 and
the hydraulic pump motor 30.
According to the present invention, the flow rate control valve 35
of the hydraulic control device may be of a type.
The hydraulic control device according to the present invention may
be adapted for use in a battery-powered forklift truck.
Alternatively, the hydraulic control device of the present
invention may be adapted for use in an engine-driven forklift truck
or a hybrid forklift truck.
* * * * *